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Date: Wed, 6 Dec 2017 13:59:25 +0100 From: Jiri Olsa <jolsa@...hat.com> To: Mengting Zhang <zhangmengting@...wei.com> Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, acme@...hat.com, huawei.libin@...wei.com, wangnan0@...wei.com, cj.chengjian@...wei.com Subject: Re: [PATCH] perf evsel: Enable ignore_missing_thread for pid option On Tue, Dec 05, 2017 at 05:03:33PM +0800, Mengting Zhang wrote: > While monitoring a multithread process with pid option, perf sometimes > may return sys_perf_event_open failure with 3(No such process) if any > of the process's threads die before we open the event. However, we want > perf continue monitoring the remaining threads and do not exit with error. > > Here, the patch enables perf_evsel::ignore_missing_thread for -p option > to ignore complete failure if any of threads die before we open the event. > But it may still return sys_perf_event_open failure with 22(Invalid) if we > monitors several event groups. > > sys_perf_event_open: pid 28960 cpu 40 group_fd 118202 flags 0x8 > sys_perf_event_open: pid 28961 cpu 40 group_fd 118203 flags 0x8 > WARNING: Ignored open failure for pid 28962 > sys_perf_event_open: pid 28962 cpu 40 group_fd [118203] flags 0x8 > sys_perf_event_open failed, error -22 > > That is because when we ignore a missing thread, we change the thread_idx > without dealing with its fds, FD(evsel, cpu, thread). Then get_group_fd() > may return a wrong group_fd for the next thread and sys_perf_event_open() > return with 22. oops, nice catch SNIP > +static int group_fd__remove(struct perf_evsel *evsel, > + int nr_cpus, int cpu_idx, > + int nr_threads, int thread_idx) please call this something more generic like update_fds, I think it affects more stuff than just group_fds > +{ > + struct perf_evsel *pos; > + struct perf_evlist *evlist = evsel->evlist; > + > + if (nr_cpus < 1 || nr_threads < 1) > + return -EINVAL; we already have check for threads->nr == 1 in ignore_missing_thread also not sure how possible is to get nr_cpus < 1, but ok > + > + if (cpu_idx >= nr_cpus || thread_idx >= nr_threads) > + return -EINVAL; > + > + evlist__for_each_entry(evlist, pos) { > + if (pos != evsel) { > + for (int cpu = 0; cpu < nr_cpus; cpu++) > + for (int thread = thread_idx; thread < nr_threads; thread++) > + FD(pos, cpu, thread) = FD(pos, cpu, thread + 1); > + } > + else { > + for (int cpu = 0; cpu < cpu_idx; cpu++) > + for (int thread = thread_idx; thread < nr_threads; thread++) > + FD(pos, cpu, thread) = FD(pos, cpu, thread + 1); > + break; > + } > + } could you please put this into some generic function, like: void perf_evsel__remove_thread(evsel, nr_cpus, nr_threads, int thread_idx) { for (int cpu = 0; cpu < nr_cpus; cpu++) for (int thread = thread_idx; thread < nr_threads; thread++) FD(pos, cpu, thread) = FD(pos, cpu, thread + 1); } with the loop would be like: evlist__for_each_entry(evlist, pos) { int nr_cpus = pos != evsel ? nr_cpus : cpu_idx; perf_evsel__remove_thread(evsel, nr_cpus, nr_threads, thread_idx) } or something along those lines... thanks for catching this jirka
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